Abstract Neuroblastoma (NB), the most frequent extracranial solid tumor in children, is involved in 15% of pediatric cancer deaths. Greater than 50% of all NB patients present with aggressive metastatic disease. Significantly, the death rate for patients that have metastatic disease at the time of diagnosis remains at around 30 to 50%, despite aggressive treatment and significant increases in our understanding of the disease. Several genetic abnormalities have been identified in this disease. However, although we have much to learn about how these genetic alterations contribute to tumor formation and metastasis, we do know that N-myc amplification and 1p36 LOH correlate with aggressive metastatic disease. Our laboratory discovered that neuroblastoma cell lines and patients frequently exhibit loss of caspase-8 expression either by epigenetic mechanisms or, in a few cases, through gene deletion. We have also shown that the loss of caspase-8 facilitates metastasis via the prevention of integrin-mediated cell death and decreases the responsiveness of neuroblastoma tumor cells to apoptotic stimuli. The studies in this proposal are designed to test the hypotheses that caspase-8 plays other non-apoptotic roles in tumorigenesis and metastasis and that caspase-8 loss and N-myc amplification/overexpression are cooperating events in tumor formation and/or metastasis. We further hypothesize that other genetic events, such as 1p36 LOH, augment tumor formation and metastasis and that these additional genetic events influence the responsiveness of NB to chemotherapeutic agents. To test these hypotheses we propose to perform studies designed to: 1) understand the biological role of caspase-8 in NB cell metastasis 2) determine the consequences of CASP8 silencing in relationship to MYCN amplification/overexpression and 1p36 LOH in neuroblastoma, and 3) determine the combined effects(s) of these genetic events on apoptosis, tumor cell proliferation, metastasis and response to chemotherapeutic agents. Upon completion of these studies we will have obtained significant new insight into the biology of this complex disease that can be used to develop more targeted treatments and ideally improve the prognosis of NB patients diagnosed with aggressive metastatic disease. In addition, since loss of caspase- 8 has been correlated with poor prognosis in medulloblastoma and with relapsed aggressive glioblastoma, both of which frequently also exhibit N-myc amplification and/or over-expression, the data from these studies may provide insight into other human tumor types.